Of the many studies done on the effects of irradiation, few have been done on the structures associated with the oral cavity. This has led to a paucity of information concerning the early and late affects of irradiation on the salivary glands. Consequently, the salivary glands represent organs which are often irradiated, both during diagnostic and therapeutic procedures, but whose actual radiosensitivity remains unclear. Following x-irradiation with 400, 800, 1600 and 6400 R parotid glands have been studied morphologically (with the electron microscope) as well as for amylase content (biochemically) and gland weight. Morphologic damage which occurs within hours following x-ray exposures as low as 800 R is accompanied by declines in gland weight and amylase content within the week following irradiation. However, the reduction in amylase may be reversed, in the injured gland, following stimulation by the secretogogue isoproterenol, as the gland resynthesizes the evacuated amylase. Current research is into the status of the secretory mechanism in the irradiated parotid acinar cell utilizing the techniques of computerized morphometric analysis to evaluate quantitatively alterations in the subcellular organelles especially with respect to the zymogen granules and Golgi zones. Accompanying these studies we are seeking to evaluate the path and kinetics of protein synthesis in the irradiated acinar cell by using H3-leucine as a marker for newly synthesized protein (in vitro) utilizing EM-autoradiography.